Currently available and well known plastic-lined piping products comprise a family of pipes, fittings, and valves especially designed for handling corrosive or high purity liquids. Such products generally comprise steel lined with a polymeric material. Such materials include, but are not limited to polyvinylidene chloride, polypropylene, polyvinylidene fluoride (PVDF), perfluoroalkoxy copolymer, fluorinated ethylene-propylene copolymer, ethylene trifluoroethylene, ethylchlorotrifluoroethylene, and polytetrafluoroethylene. Such products enjoy both the structural integrity of steel and the high chemical resistance characteristic of the selected polymeric liner.
Typically, each pipe, fitting, valve, etc. will contain a flange at or substantially near each end thereof. Adjacent pipes, fittings, valves, etc., within a given pipeline may be joined one to another by the fastening together of such flanges, e.g., by bolting.
While flanged joints are acceptable in most applications, advantage could be had in flangeless joints. Such joints could be constructed to be fluid-proof and vapor-proof, to decrease (if not eliminate) fugitive emissions through the joints. Moreover, such joints would be less bulky than flanged joints, which would make their enclosure within secondary containment systems less unwieldy.
In WO 95/12086 a flangeless pipe joint is disclosed. The disclosed flangeless joints were designed for plastic-lined pipe systems, wherein adjacent plastic liners are joined together by joining means other than compressive force to form a fluid and vapor tight seal between the liners. The disclosure provided for joints in which the linear movement of the polymeric liners was restrained, and which could also be equipped with a secondarily contained leak detection zone for detecting leaks in the joining means.
While these joints successfully join sections of pipe, flanges are still needed to connect the pipe to fittings such as elbows, crosses, tees, laterals, reducers, and other similar types of fittings. The absence of fittings for flangeless piping system is primarily a result of the manufacturing process. Plastic-lined process pipe typically falls into one of three subcategories: loose-lined pipe, interference fit pipe, and swaged pipe.
Loose-lined pipe is characterized by a polymeric liner retained within a pipe only at the points of joinder between adjacent pipe segments, wherein the outside liner diameter is at least about 97 percent of the inside diameter of the pipe segment. Loose-lined pipes are typically manufactured by slipping a pre-formed polymeric liner into a flanged pipe segment, flaring the liner over the structurally rigid flange face, and bolting the flange to an adjacent flange. In loose-lined pipe, the liner is thus retained within the pipe segment by the compressive force exerted on the flared portion of the liner at the flange face. Loose-lined pipe is generally sold as its components, e.g., as pipe segments, polymeric liners, and flanges. In the field, the liner may be inserted into the flanged pipe segment, and may be flared as described above.
Interference fit pipe, which is also known as reverse swaged pipe, is characterized by a zero tolerance fit between the polymeric liner and the pipe segments. Interference fit plastic-lined pipe is typically formed by compressing a preformed polymeric liner having an outer diameter greater than the inner diameter of the pipe segment by passing it through a sizing die, and inserting the compressed liner into the pipe segment before the liner expands. Upon the release of the force by which the liner is pulled through the pipe, the memory of the plastic causes the liner to exert force upon the inner wall of the pipe segment, serving to assist in retaining the liner within the pipe segment. Due to the special apparatus required to achieve the interference fit relationship, interference fit pipe is generally available as pre-lined pipe segments.
Swaged pipe is characterized by a zero tolerance fit between the polymeric liner and the pipe segments. Swaged pipe is typically formed by inserting a preformed polymeric liner into an oversized pipe segment and physically compressing both the pipe and the liner under tremendous pressure such that the liner and the pipe segment are reduced in size to the finished diameters. To further facilitate retention of the liner within the pipe segment, pipe segments to be lined may be "picked" to provide barbs and recessed portions into which the liner is directed during swaging. Due to the special apparatus required to swage pipe, swaged pipe is generally available as pre-lined pipe segments.
Thus, it can be seen that in plastic-lined piping systems the liner is preformed then inserted into the pipe by some means. While this is possible for straight sections of pipe, it is not feasible for fittings with bends and/or additional legs. Thus, typically these types of parts are formed by injection molding. Current methods of injection molding, however, do not produce a zero tolerance fit between the liner and the pipe. Zero tolerance fit piping systems tend to better retain the liner in close proximity with the metal, thus limiting the extent of expansion and retraction of the liner during temperature cycling such as when temperature changes within the piping or when extreme ambient temperatures are encountered. Zero tolerance fit between the liner and the metal also anchors the liner so that it may more easily be prepared for butt welding and to facilitate making the butt weld itself, should that method be used to join the fitting to plastic-lined piping.
Another problem encountered with flangeless joining of current injection molded plastic-lined fittings to zero tolerance plastic-lined piping is that the liner of the fitting does not match up with the liner of the pipe, making it difficult or impossible to securely join the liners. This is because the liner of the pipe is under pressure from either the swaging or reversed swaging process. Thus, where the pipe does not contain the liner, that is, where the liner extends past the pipe, the liner expands outward. In current injection molded plastic lined fittings there is no pressure on the liners, so there is no outward expansion where the liner extends past the metal of the fitting. Accordingly, the liner for a fitting made following current procedures will not align with the liner for the pipe, despite the pipe and the fitting being of the same internal diameter.
It would therefore be desirable to have fittings which could be joined without flanges to the flangeless plastic-lined piping systems contemplated by WO 95/12086, while providing for the liner to be anchored to the pipe fitting in a zero tolerance fit. Accordingly, it is an object of the the subject invention to provide such a fitting.
One aspect of the present invention is a fitting comprising:
a. a section of pipe having two or more legs, each leg terminating in an opening such that fluid may flow through the section of pipe, wherein each leg has an outside diameter and an inside diameter, and wherein the inside diameter terminates at each opening in a chamfered surface such that an angle q is formed between the the chamfered surface and the inside diameter; PA1 b. a liner made from a plastic material which is capable of being injection molded and which shrinks upon cooling following injection molding; the liner having an outside diameter and an inside diameter, the liner extending through the section of pipe such that a portion of the liner extends past each opening; PA1 wherein the outside diameter of the liner in the portion which extends past each opening is larger than the inside diameter of respective leg; and PA1 wherein q is greater than or equal to the inverse tangent of the shrink in the liner radius from just after injection molding until cool, divided by the lengthwise shrink of the liner from just after injection molding until cool. PA1 a. providing a section of pipe having two or more legs, each leg terminating in an opening such that fluid may flow through the section of pipe, wherein each leg has an outside diameter and an inside diameter, and wherein the inside diameter terminates at each opening in a chamfered surface such that an angle q is formed between the the chamfered surface and the inside diameter; PA1 b. inserting a mandrel through the openings, the mandrel having an outside diameter that is less than the inside diameter of each leg such that a plastic material may be injected between the outside diameter of the mandrel and the inside diameter of each leg so that a lining of desired thickness will be formed; PA1 c. providing a cap means extending past the ends of the legs, said cap means having an inside diameter which is larger than the inside diameter of the leg; PA1 d. injecting melted plastic material into the space between the mandrel and the inside diameters of the legs and cap means; PA1 e. removing the cap means and the mandrel; and PA1 f. allowing the plastic to cool whereby the newly formed liner shrinks and as the liner shrinks the larger outside diameter sections formed by the cap means are pulled tight against the chamfered surface such that it forms a zero tolerance fit; PA1 wherein the angle q is greater or equal to the inverse tangent of the shrink in the liner radius from just after injection molding until cool divided by the lengthwise shrink of the liner from just after injection molding until cool.
Another aspect of the present invention is a process of preparing a plastic lined fitting comprising:
For a more complete understanding of the invention, reference should be made to the Detailed Description of the Invention, which makes reference to the following drawings: